In a Long Term Evolution-Advance (LTE-Advance) system, to improve coverage of a cell edge, a radio access network of an original Long Term Evolution (LTE) is expanded, and a relay technology is introduced. In the relay technology, a relay node (RN) is used to provide radio services for a user equipment (UE), which increases quality of communication between the UE and a DeNB. In addition, each RN has only one donor eNB (DeNB).
Communication between the RN and the DeNB is implemented by using a backhaul link (backhaul link), and communication between the RN and the UE is implemented by using an access link (access link). The backhaul link and the access link can separately implement, by using a half-duplex frequency division duplex (H-FDD) mode, data transmission between the RN and the DeNB and between the RN and the UE. The H-FDD is another duplex mode relative to a current frequency division duplex (FDD). Like the FDD mode, the H-FDD mode uses different frequency bands in an uplink channel and a downlink channel, and uses a paired spectrum. In H-FDD mode, a frame structure mode of the FDD may still be used, and there is only a slight difference between the H-FDD mode and the FDD mode during implementation of a physical layer in a radio interface protocol stack. However, at a MAC layer and a physical layer of the radio interface protocol stack, radio resources need to be allocated properly according to a sending manner and a receiving manner of the H-FDD.
When both the DeNB and the RN use the H-FDD mode, in the downlink channel, the DeNB and the RN separately send information to the RN and the UE by using different subframes. Similarly, in the uplink channel, the DeNB and the RN also separately receive, by using different subframes, information sent by the RN and the UE. This manner of receiving and sending information by using different subframes can avoid mutual interference between the access link and the backhaul link. In a process of accessing the DeNB by the RN, the DeNB sends an RN reconfiguration message (RN_RECFG message) to the RN in FDD mode. The RN receives the RN_RECFG message in FDD mode, and configures, according to the RN_RECFG message, communication parameters in an RN-side radio interface protocol stack to prepare for communication with the DeNB.
In the prior art, when the DeNB is in H-FDD mode, the DeNB sends information to the RN by using a downlink control channel allocated to the RN, which may also be referred to an RN-side physical downlink control channel (R_PDCCH channel). Using one frame structure as an example, the R_PDCCH channel occupies several resource blocks in a frequency domain, and a position occupied by the R_PDCCH channel in a time domain is a position after a length of symbols occupied by a PDCCH channel is deducted.
For example, the RN receives, in a physical downlink control channel (PDCCH channel), a scheduling message sent by the DeNB, and receives an RN_RECFG message according to the scheduling message. After finishing configuring the communication parameters in the RN-side radio interface protocol stack, the RN enters an H-FDD state and receives and sends data in H-FDD mode. At this time, the RN can only receive downlink resource allocation information of the DeNB in the R_PDCCH channel, and cannot receive downlink resource allocation information of the DeNB in the PDCCH channel.
After finishing configuring the communication parameters in the RN-side radio interface protocol stack, the RN generates an RN reconfiguration completion message (RN Reconfiguration Completion, hereinafter abbreviated as RN_RECFG_CMP message). At this time, the RN has already entered the H-FDD state, and the RN reports the RN_RECFG_CMP message to the DeNB in H-FDD mode. In the prior art, the DeNB sends a scheduling message of the RN_RECFG_CMP message to the RN, where the scheduling message includes a subframe position that is allocated to the RN and used to send the RN_RECFG_CMP message to the DeNB. After receiving the scheduling message, the RN sends, at the subframe position, the RN_RECFG_CMP message to the DeNB.
However, the foregoing process may have the following risks.
In a first case, before the DeNB sends a scheduling message of the RN_RECFG_CMP message to the RN, the RN has already switched to the H-FDD state, but the DeNB is still in an FDD state. At this time, the DeNB may still send a scheduling message of the RN_RECFG_CMP message in the PDCCH channel. Because the RN has already switched to the H-FDD state at this time, the RN can only obtain the downlink resource allocation information sent by the DeNB in the R_PDCCH channel, and cannot receive the downlink resource allocation information sent by the DeNB in the PDCCH channel. As a result, the RN cannot receive the scheduling message sent by the DeNB, and further the RN cannot send the RN_RECFG_CMP message to the DeNB.
In a second case, when the RN receives, in FDD mode and in the PDCCH channel, the RN_RECFG message sent by the DeNB in FDD mode, the RN sends a radio link control acknowledgement message (Radio Link Control Acknowledge message, abbreviated as RLC ACK message) to the DeNB. At this time, if the DeNB has already switched to the H-FDD state but the RN is still in the FDD state, the DeNB can only receive messages sent by the RN in some subframes; if the RLC ACK message sent by the RN to the DeNB is located in other subframes, the RL ACK message cannot be received by the DeNB. Therefore, the DeNB cannot receive the RLC ACK message sent by the RN, and as a result, the RN cannot access a network or accesses the network abnormally.